A mobile terminal apparatus such as a mobile telephone has a microphone buried into a casing. For example, a mobile telephone handset used by sliding the display section casing with respect to the operation section casing has a microphone sound hole disposed on the bottom surface of the operation section casing. For this reason, if a call is made with the main unit in the retracted state, the voice of the other party coming from the speaker travels around the upper part of the display section casing and enters into the gap between the display section casing and the operation section casing. The voice of the other party that enters the gap, by being reflected between the two casings, easily enters the microphone, resulting in a phenomenon whereby the other party can hear his or her own voice (hereinafter referred to as an echo).
When coupling of sound or vibration occurs between the speaker and the microphone, an echo occurs whereby the voice of the other party returns to his or her own ear.
Patent Literature 1 describes a mobile telephone handset in which the display section casing can be slid with respect to the operation section casing. The mobile telephone handset described in Patent Literature 1 is provided with a protrusion in the display section casing direction in the periphery of the microphone installed in the operation section casing. In addition, the mobile telephone handset is provided with a protruding section in the operation section casing direction in the display section casing part opposing the protruding section of the above-noted operation section casing when the slide in the collapsed condition. With this configuration, a wall is formed around the microphone by the two opposing protrusions, which suppresses the occurrence of echoes during a call.